pv s y s tem de s i g n and yield s im u lati o n s f o r a farm in ry gg e m u ni c ipality
s y s temde s i g n av so l c elleanle gg og
pr o d u k sjo n ss im u lerin g er f o r en g ård i ry gg e k o mm u ne
andrea s madland s t ø rdal
DepartmentofmathematicalsciencesandtechnologyMasterThesis30credits2013
Preface'
This!thesis!was!carried!out!in!order!to!investigate!the!possibility!of!installing!a!roof!photovoltaic!
(PV)!system!on!a!farm!in!Rygge.!Thousands!of!farms!exist!in!Norway!today,!and!many!of!these!
have! in! common! that! they! have! high! electricity! consumption! and! large! roof! surfaces.! These!
surfaces!could!be!utilized!for!power!production!by!installing!a!PV!system,!which!would!provide!
clean,!locally!produced!electricity.!
!
The!thesis!was!a!part!of!a!project!initiated!by!Multiconsult!AS!where!the!different!possibilities!
for!local!energy!production!in!the!agricultural!sector!were!considered.!In!addition!to!this!thesis!
concerning!PV!systems,!two!other!master!theses!have!been!written!simultaneously,!considering!
local!windG!and!biogass!production,!respectively.!
!
I!would!like!to!thank!my!supervisor,!Dr.Ing!Espen!Olsen,!for!his!assistance!during!my!work!on!
this! thesis.! He! has! contributed! through! discussions,! by! assisting! in! the! search! for! relevant!
information!and!with!his!general!insight!into!the!PV!industry.!
!
Furthermore,! I! would! like! to! thank! Dr.Ing! Bjørn! Thorud,! coGsupervisor! and! Head! of! Solar! at!
Multiconsult,! and! Siv! Helene! Nordahl,! consultant! at! the! same! company.! Bjørn! initiated! this!
thesis,! and! provided! with! me! answers! to! technical! and! economical! questions! regarding! PV!
systems.!He!also!gave!me!a!great!start!to!this!project!by!inviting!me!to!a!twoGday!course!in!PV!
system!design.!Siv!Helene!helped!me!particularly!in!the!work!with!the!simulation!software!used!
in!the!thesis,!and!also!answered!technical!questions!regarding!PV!system!design.!
!
I! would! also! like! to! thank! Per! Olaf! Roer! for! letting! me! use! his! farm! as! a! case! study,! and! for!
providing!me!with!all!the!information!I!needed!regarding!technical!specifications!on!the!farm.!
!
Finally,! I! would! like! to! thank! my! friends!and! colleagues! at! room! TF209! for! many! good! laughs!
and!interesting!discussions!during!this!semester.!
!
Ås,!May!13th!2013!
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Andreas!Madland!Størdal!
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Abstract'
In!this!thesis,!the!possibility!of!installing!a!roof!PV!system!on!a!farm!in!Rygge,!Norway!has!been!
evaluated.! The! farm! has! electricity! consumption! equivalent! to! about! eight! Norwegian!
households,!and!several!large,!southward!facing!roof!surfaces.!!
!
Meteorological!data!for!the!area!has!been!assessed!in!order!to!determine!the!resource!base!for!
solar! power! production.! The! collection! process! has! revealed! that! the! amount! of! irradiation! in!
this!area!is!uncertain,!and!different!sources!provide!different!values!with!respect!to!the!amount!
of! irradiation! in! the! area.! In! the! main! simulations,! irradiation! data! from! a! weather! station!
located! approximately! 30! kilometres! from! the! farm! was! used.! The! data! from! this! weather!
station! suggest! that! the! annual! irradiation! on! the! horizontal! plane! is! approximately! 880!
kWh/m2.!
!
Different! factors! that! affect! the! performance! of! a! PV! system! have! been! evaluated,! including!
module!orientation,!shading!and!efficiency!losses.!A!shade!analysis!for!the!different!roofs!on!the!
farm!has!been!made.!The!analysis!shows!that!there!is!limited!shading!on!the!farm!roofs,!and!that!
shading!losses!mainly!occur!during!winter!when!irradiance!levels!are!low.!
!
The!simulation!software!PVsyst!have!used!to!design!and!simulate!several!PV!systems!for!each!of!
the! three! largest! roofs! on! the! farm.! Different! moduleG! and! inverter! types! were! used! in! the!
simulations!in!order!to!find!the!bestGperforming!system!for!each!roof.!All!the!bestGperforming!
systems! included! REC! modules.! Two! systems! included! inverters! from! Eltek! Valere,! while! one!
system!included!inverters!from!SMA.!
!
The!simulations!show!that!systems!with!a!combined!peak!power!of!105.5!kWp!could!be!installed!
on!the!three!largest!roofs!on!the!farm.!!The!simulated!specific!yield!for!the!three!roofs!was!821!
kWh/kWp! year,! and! the! combined! production! was! 86! 607! kWh/year.! The! production! would!
cover!50%!of!the!local!consumption!in!2012.!
!
The!amount!of!installed!PV!systems!in!Norway!is!limited,!and!several!of!the!parameters!used!in!
the!simulations!are!therefore!subject!to!uncertainties.!Additional!simulations!were!performed!in!
order!to!investigate!the!sensitivity!in!system!performance!to!a!change!in!three!key!parameters:!
Irradiation!data,!soiling!losses!and!module!UGvalue.!!The!sensitivity!analysis!shows!that!a!change!
of! source! for! the! irradiation! data! could! affect! the! simulated! system! performance! by! 15%.! ! A!
change! in! soiling! loss! settings,! mainly! determined! by! snow! cover! on! the! modules,! could! also!
have!significant!impact!on!the!simulated!system!yield.!The!impact!of!change!in!the!module!UG value!on!the!simulation!results!was!limited.!!
!
The! simulated! production! is! not! very! well! correlated! with! the! local! consumption.! The! larger!
fraction!of!the!production!will!occur!during!spring!and!summer,!while!a!large!part!of!the!local!
consumption! takes! place! during! fall! and! winter.! The! construction! of! a! roof! PV! system! will!
therefore! lead! to! an! export! situation! during! parts! of! the! summer! months,! where! some! of! the!
electricity! will! be! supplied! to! the! grid.! The! farmer! would! then! become! a! part! of! the! surplus!
customer!arrangement.!
!
An!economical!evaluation!of!the!different!systems!shows!that!the!Net!Present!Value!(NPV)!of!all!
the!simulated!systems!is!negative.!The!lowest!real!levelized!cost!of!electricity!(LCOE)!has!been!
estimated!to!1.47!NOK/kWh.!!There!are!large!uncertainties!in!the!economical!evaluation!of!the!
systems!due!to!the!immature!market!for!such!systems!in!Norway,!and!the!previously!mentioned!
uncertainties!with!respect!to!system!performance.!
Sammendrag'
I! denne! oppgaven! har! muligheten! for! å! installere! et! PVGsystem! på! en! gård! i! Rygge! blitt!
undersøkt.!Gården!har!et!elektrisitetsforbruk!som!tilsvarer!ca.!8!norske!husstander,!og!har!flere!
store,!sørvendte!tak.!!
!
Værdata!har!blitt!samlet!inn!for!området!for!å!kunne!vurdere!ressursgrunnlaget!for!produksjon!
av! solstrøm.! Innsamlingsprosessen! har! avslørt! at! mengden! solinnstråling! i! dette! området! er!
usikker,! og! ulike! kilder! gir! ulik! informasjon! med! hensyn! til! årlig! mengde! solinnstråling.! I!
simuleringer!utført!i!oppgaven!er!det!brukt!innstrålingsdata!fra!en!værstasjon!30!kilometer!fra!
gården.!Data!fra!denne!værstasjonen!indikerer!at!årlig!innstråling!på!horisontalplanet!er!ca.!880!
kWh/m2.!
!
Ulike!faktorer!som!påvirker!et!PVGsystems!ytelse!har!blitt!vurdert,!inkludert!modulorientering,!
skygging!og!effektivitetstap.!En!skyggeanalyse!for!stedet!har!blitt!gjennomført,!og!denne!viser!at!
skyggetap!i!hovedsak!oppstår!i!vintermånedene!når!innstrålingsnivåene!er!lave.!
!
Simuleringsprogrammet!PVsyst!er!blitt!brukt!til!å!designe!og!simulere!ulike!systemer!for!hvert!
av! de! tre! største! takene! på! gården.! Ulike! moduler! og! vekselrettere! har! blitt! brukt! i!
simuleringene! for! å! kunne! finne! et! optimalt! system! for! hvert! tak.! Alle! de! tre! systemene! som!
hadde! best! ytelse! i! simuleringene! inneholdt! moduler! fra! REC.! To! av! systemene! innehold!
vekselrettere!fra!Eltek!Valere,!mens!et!system!innehold!vekselrettere!fra!SMA.!
!
Simuleringene! viser! at! systemer! med! en! samlet! effect! på! 105.5! kWp! kan! installeres! på! de! tre!
største!takene!på!gården.!Den!spesifikke!produksjonen!for!systemene!vil!være!821!kWh/kWp,!
noe!som!gir!en!samlet!årlig!produksjon!på!86!607!kWh.!Dette!tilsvarer!50%!av!gårdens!samlede!
forbruk!i!2012.!
!
Det!er!et!begrenset!antall!PVGsystemer!installert!i!Norge!i!dag,!og!mange!av!parameterne!som!er!
brukt! i! simuleringene! er! derfor! usikre.! Oppfølgingssimuleringer! ble! derfor! gjennomført! for! å!
vurdere!konsekvensen!av!en!endring!i!tre!nøkkelparametere:!Innstrålingsdata,!tildekkingstap!og!
modulens! UGverdi.! En! sensitivitetsanalyse! viser! at! bruk! av! en! annen! kilde! for! innstrålingsdata!
kan! endre! systemets! årlige! simulerte! produksjon! med! 15%.! En! endring! i! innstillingene! for!
tildekkingstap,!som!i!hovedsak!skyldes!snø!på!modulene,!kan!også!ha!signifikant!innvirkning!på!
simuleringsresultatene.! En! endring! i! modulenes! UGverdi! hadde! en! begrenset! innvirkning! på!
simuleringsresultatene.!
!
Den!simulerte!årlige!produksjonen!er!dårlig!korrelert!med!det!lokale!forbruket!på!gården.!Den!
største! delen! av! produksjonen! foregår! i! vårG! og! sommermånedene,! mens! den! største! delen! av!
forbruket!finner!sted!i!høstG!og!vintermånedene.!En!eventuell!bygging!av!et!PVGsystem!vil!derfor!
føre! til! at! gården! havner! i! en! eksportsituasjon! i! deler! av! sommermånedene,! hvor! produsert!
elektrisitet! vil! leveres! til! strømnettet.! I! et! slikt! tilfelle! vil! gården! bli! en! del! av!
plusskundeordningen.!
!
En! økonomisk! vurdering! av! anleggene! viser! at! netto! nåverdi(NNV)! er! negativ! for! alle! de!
simulerte! systemene.! Den! laveste! beregnede! elektrisitetskostnaden! er! 1.47! NOK/kWh.! Det! er!
store! usikkerheter! knyttet! til! den! økonomiske! vurderingen! av! anleggene! på! grunn! av! det!
umodne!markedet!for!slike!systemer!i!Norge,!samt!de!tidligere!nevnte!usikkerhetene!knyttet!til!
produksjonen!fra!systemet.!
!
!!
!
Contents'
Preface!...!i!
Abstract!...!ii!
Sammendrag!...!iii!
Contents!...!iv!
List!of!figures!...!v!
List!of!tables!...!vii!
List!of!symbols!...!viii!
Abbreviations!...!x!
1.!Introduction!...!1!
1.1!Motivation!...!1!
1.2!Objectives!and!Limitations!...!1!
1.3!The!Farm!...!1!
1.4!Outline!...!2!
2.!Components!in!GridGconnected!PV!Systems!...!3!
2.1!Solar!Cells!and!Modules!...!3!
2.2!Inverters!...!8!
2.3!DC!and!AC!Cables!...!10!
2.4!Mounting!Systems!...!11!
2.5!Other!BoS!Components!...!11!
3.!Theory:!Design!and!Optimization!of!GridGconnected!PV!systems!...!13!
3.1!Site!Assessment!...!13!
3.2!Solar!Radiation!and!Meteorology!...!13!
3.3!Module!Orientation!...!19!
3.4!Shading!Effects!on!PV!Systems!...!20!
3.5!System!Design!and!Component!Selection!...!22!
3.6!System!Losses!and!System!Performance!...!26!
3.7!Economical!Evaluation!of!PV!Systems!...!30!
4.!Methodology:!Design!and!simulation!of!PV!systems!...!34!
4.1!PVsyst!...!34!
4.2!Site!Assessment!...!35!
4.3!Meteorological!Data!...!40!
4.4!Module!Orientation!...!47!
4.5!Shade!Analysis!...!49!
4.6!System!Design!and!Component!Selection!...!53!
4.7!System!Losses!...!58!
4.8!Sensitivity!Analysis!...!61!
4.9!Economical!Evaluation!...!62!
5.!Simulation!Results!and!Economical!Evaluation!...!65!
5.1!System!Performance!...!65!
5.2!Sensitivity!Analysis!G!Irradiation!Data!...!73!
5.3!Sensitivity!Analysis!G!Soiling!Losses!...!75!
5.4!Sensitivity!Analysis!–!Module!UGvalue!...!77!
5.5!Comparison!of!Production!and!Consumption!...!78!
5.6!Economical!Evaluation!...!80!
6.!Conclusion!...!84!
7.!Further!Work!...!85!
8.!References!...!86!
Appendix!A:!Meteorological!Data!...!89!
Appendix!B:!Shade!Analysis!...!95!
Appendix!C:!Component!Specifications!...!99!
Appendix!D:!Simulation!Results!...!111!
Appendix!E:!Economical!Evaluation!...!118!
List'of'figures'
Figure!1:!Panorama!of!the!farm.!...!2
!
Figure!2:!Schematic!of!a!gridGconnected!PV!system.!...!3
!
Figure!3:!Semiconductor!band!structure.!...!4
!
Figure!4:!Illustration!of!a!crystalline!solar!cell.!...!4
!
Figure!5:!The!single!diode!model!for!a!solar!cell.!...!5
!
Figure!6:!The!characteristic!curve!of!a!solar!cell.!...!6
!
Figure!7:!A!solar!cell,!a!module,!a!string!and!an!array.!...!6
!
Figure! 8:! Characteristic! curves! for! a! solar! module! under! different! irradiance! conditions.! From! PVsyst[7].!...!7
!
Figure! 9:Characteristic! curves! for! a! solar! module! for! different! operating! temperatures.! From! PVsyst[7].!...!7
!
Figure!10:!Efficiency!curves!for!an!SMA!inverter!for!different!voltage!levels[11].!...!9
!
Figure!11:!Central!inverter!configuration.!...!9
!
Figure!12:!String!inverter!configuration.!...!10
!
Figure!13:!Module!inverter!configuration.!...!10
!
Figure!14:!Illustration!of!a!PV!mounting!system!for!tiled!roofs[12].!...!11
!
Figure!15:!Schematic!of!the!net!metering!system!and!the!gross!metering!system.!...!12
!
Figure!16:!The!Earth´s!declination!angle!for!different!times!of!the!year.!...!14
!
Figure!17:!Illustration!of!the!elevation!angle!h.!...!15
!
Figure!18:!Illustration!of!the!Air!Mass!(AM)!concept.!...!16
!
Figure!19:!Irradiance!spectrum!for!extraterrestrial!irradiance!and!irraance!at!AM1.5[13].!...!16
!
Figure!20:Different!components!of!solar!radiation.!...!17
!
Figure!21:!Irradiance!values!registered!on!March!14th!at!a!weather!station!in!Ås.!...!18
!
Figure!22:!Map!from!PVGIS!showing!average!global!irradiation!values!for!Europe[14].!...!18
!
Figure!23:!The!azimuth!angle!and!tilt!angle.!...!19
!
Figure!24:!Electrical!characteristic!of!a!module!with!one!shaded!cell.!From!PVsyst![7].!...!21
!
Figure!25:!HotGspot!formation!in!a!shaded!solar!cell!in!series!with!other!nonGshaded!cells.!...!21
!
Figure!26:Schematic!of!a!PV!module!with!36!cells!connected!in!series!and!two!bypass!diodes.!..!22
!
Figure! 27:Electrical! characteristic! of! a! module! with! one! shaded! cell! and! three! bypass! diodes.! From!PVsyst.[7].!...!22
!
Figure!28:!The!MPPT!and!voltage!range!of!an!inverter.!From!PVsyst[7].!...!24
!
Figure!29:!Reflection!of!irradiance!due!to!low!incidence!angle.!...!27
!
Figure!30:!Efficiency!of!a!crystalline!module!at!different!irradiance!levels.!From!PVsyst[7].!...!28
!
Figure! 31:! Efficiency! of! a! crystalline! module! for! different! operating! temperatures.! From! PVsyst[7].!...!28
!
Figure!32:!Price!development!for!electricity!certificates!in!2012.!...!31
!
Figure!33:!Flow!chart!of!the!methodology!used!in!this!thesis.!...!34
!
Figure!34:!3D!illustration!of!the!farm!made!in!PVsyst.!...!36
!
Figure! 35:! SouthwardGfacing! roofs! on! the! chicken! house(upper! left),! the! grain! storage! building(upper!left),!the!garage(lower!left)!and!the!vegetable!storage!building.!...!36
!
Figure!36:!Shading!items!on!building!1.!...!37
!
Figure!37:!Shading!items!south!of!building!3.!...!38
!
Figure!38:!OnGsite!electricity!consumption!in!2011!and!2012.!...!39
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Figure!39:!Relative!load!duration!in!2011!and!2012.!...!39
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Figure!40:!OnGsite!electricity!consumption!in!2011!and!2012.!...!40
!
Figure!41:!Solar!paths!for!different!times!of!the!year!generated!in!PVsyst.!...!40
!
Figure!42:!Example!of!synthetic!hourly!irradiation!values!generated!in!PVsyst.!...!41
!
Figure!43:!Measured!values!for!annual!global!irradiation!on!the!horizontal!plane.!...!42
!
Figure!44:!Measured!values!for!monthly!global!irradiation!on!the!horizontal!plane.!...!43
!
Figure!45:!Annual!global!irradiation!on!the!horizontal!plane!from!different!databases.!...!45
!
Figure!46:!Monthly!global!irradiation!on!the!horizontal!plane!from!different!databases.!...!45
!
Figure!47:!Screen!dumps!from!the!shade!analysis!in!PVsyst.!...!50
!
Figure!48:!IsoGshading!diagram!for!building!1!generated!in!PVsyst.!...!51
!
Figure!49:!IsoGshading!diagram!for!building!3!generated!in!PVsyst.!...!51
!
Figure!50:!IsoGshading!diagram!for!building!5!generated!in!PVsyst.!...!52
!
Figure!51:!Incidence!factor!F!as!a!function!of!incidence!angle.!...!59
!
Figure!52:!Yearly!average!performance!of!system!1.2!from!PVsyst.!...!67
!
Figure!53:!Normalized!production!and!monthly!average!PR!for!system!1.2!from!PVsyst.!...!67
!
Figure!54:!Yearly!average!performance!of!system!3.2!from!PVsyst.!...!68
!
Figure!55:!Normalized!production!and!average!monthly!PR!for!system!3.2!from!PVsyst.!...!68
!
Figure!56:!Yearly!average!performance!of!system!5.2!from!PVsyst.!...!69
!
Figure!57:!Normalized!production!and!monthly!performance!ratio!for!system!5.2!from!PVsyst.!69
!
Figure!58:!Suggested!module!layout!and!string!configuration!for!system!1.2.!...!70!
Figure!59:!Suggested!module!layout!and!string!configuration!for!system!3.2.!...!70
!
Figure!60:!Suggested!string!configuration!for!system!5.2.!...!71
!
Figure!61:!Monthly!yield!from!system!3.2!for!different!meteorological!datasets.!...!74
!
Figure!62:!Monthly!simulated!production!for!system!3.2!for!different!soiling!loss!values.!...!76
!
Figure!63:!Monthly!system!yield!from!system!3.2!using!different!module!UGvalues.!...!77
!
Figure!64:!Combined!simulated!production!and!consumption.!...!79
!
Figure!65:!Sensitivity!in!LCOE!for!system!3.2.!...!81
!
List'of'tables'
Table!1:Different!types!of!solar!cells![4],![9]!and![10].!...!8
!
Table!2:!Albedo!values!for!different!surfaces[6].!...!17
!
Table!3:!Possible!locations!of!a!PV!array.!...!35
!
Table!4:!Roof!specifications!...!37
!
Table!5:!Relevant!weather!stations!in!the!Rygge!area.!...!42
!
Table!6:!Average!temperature!and!wind!speed!data.!...!43
!
Table!7:!Average!snow!depth!in!Rygge.!...!44
!
Table!8:!Databases!used!to!collect!meteorological!data!for!the!site.!...!44
!
Table!9:!Meteoset!A.!...!46
!
Table!10:!Albedo!values!used!in!the!simulations.!...!47
!
Table!11:!Module!tilt!angles!for!the!different!roofs.!...!48
!
Table!12:!Azimuth!angle!for!the!different!roofs.!...!48
!
Table!13:!Irradiation!losses!with!respect!to!optimum!tilt!and!azimuth!angle.!...!48
!
Table!14:!Percentage!shading!loss!of!direct!irradiation!for!different!dates.!...!50
!
Table!15:!Module!selection!criteria.!...!54
!
Table!16:!Cell!temperatures!for!the!selected!modules!under!different!operating!conditions.!...!55
!
Table!17:!Input!design!temperatures!for!matching!of!array!and!inverter.!...!56
!
Table!18:!Voltage!levels!for!the!selected!modules!at!different!operating!temperatures.!...!56
!
Table!19:!Minimum!and!maximum!amount!of!modules!in!a!string!for!different!module/inverter! combinations.!...!56
!
Table!20:!Combinations!of!modules!and!inverters!used!in!the!simulations.!...!57
!
Table!21:!UGvalue!factors!used!in!the!main!simulations.!...!58
!
Table!22:!DC!and!AC!cable!loss!settings!used!in!the!simulations.!...!59
!
Table!23:!Module!quality,!LID!and!mismatch!parameters!used!in!the!simulations.!...!60
!
Table!24:!Monthly!soiling!loss!values!used!in!the!main!simulations.!...!61
!
Table!25:!Yearly!average!soiling!losses!used!in!the!soiling!loss!sensitivity!analysis.!...!62
!
Table!26:!Input!parameters!used!in!the!module!UGvalue!sensitivity!analysis.!...!62
!
Table!27:!Financial!assumptions!used!in!the!NPV!calculations.!...!63
!
Table!28:!Utility!grid!tariff!for!Hafslund!commercial!customers[44].!...!63
!
Table!29:!Energy!tariff!for!Hafslund!surplus!customers[45].!...!64
!
Table!30:!Financial!assumptions!used!in!the!LCOE!calculations.!...!64
!
Table!31:!Yearly!effective!irradiation!the!PV!arrays.!...!65
!
Table!32:!System!performance!for!the!simulated!systems.!...!66
!
Table!33:!DC!cable!sizing!for!system!1.2.!...!70
!
Table!34:!DC!cable!sizing!for!system!3.2.!...!71
!
Table!35:!DCGcable!sizing!for!system!5.2.!...!71
!
Table!36:!Influence!of!meteorological!data!on!simulated!system!performance.!...!73
!
Table!37:!Influence!of!soiling!losses!on!the!simulated!system!performance.!...!75
!
Table!38:!System!performance!for!different!module!UGvalue!simulation!settings.!...!77
!
Table!39:!Monthly!production!from!the!bestGperforming!systems.!...!78
!
Table!40:!LCOE!and!NPV!calculations!for!three!of!the!systems!on!building!1.!...!80
!
Table!41:LCOE!and!NPV!calculations!for!three!of!the!systems!on!building!3.!...!80
!
Table!42:!NPV!and!LCOE!calculations!for!three!of!the!systems!on!building!5.!...!81
!
Table!43:!NPV!of!system!3.2!for!different!support!schemes.!...!81
!
!
List'of'symbols'
!
Symbol Explanation Unit
A Area m2'or'mm2
b0 Module'incidence'constant /
Ct Cash'flow'in'year't NOK
Eg Energy'band'gap J'or'eV
FIAM Array'incidence'factor C
Gex Extraterrestrial'irradiance W/m2
Ginc Inclined'plane'irradiance W/m2
GNOCT NOCT'irradiance W/m2
HG Global'irradiation Wh/m2/day
HB Direct'beam'irradiation Wh/m2/day
HD Diffuse'irradiation Wh/m2/day
Hp Plane'irradiation Wh/m2/day
HR Reflected'irradiation Wh/m2/day
h The'Planck'constant Js
hs Solar'elevation o
I Electric'current A
Icable Cable'current A
ID Diode'current A
Igen Generated'current A
IL Load'current A
IMPP Current'at'MPP A
IRP Leakage'current' A
Isc ShortCcircuit'current A
It Income'in'year't NOK
i Incidence'angle o
i Discount'rate %
l Length m
nmin Minimum'amount'of'modules'in'a'string C nmax Maximum'amount'of'modules'in'a'string C
Ot Cash'outflow'in'year't NOK
P Power W
Pcell Cell'power W
Pt Present'value'of'cashflow'in'year't NOK
Pcable Ohmic'cable'loss W
R Transposition'factor C
Rcable Cable'resistance Ω
!
Symbol Explanation Unit
RL Load&resistance Ω
RRP Leakage&resistance Ω
RS Series&resistance Ω
S0 The&solar&constant W/m2
Sex The&instantaneous&solar&constant W/m2
TA Ambient&temperature oC
TSTC Temperature&at&STC oC
Tz Cell&temperature oC
U Thermal&loss&factor W/m2&K
Uc Constant&thermal&loss&factor W/m2&K
Uv Vind&dependent&thermal&loss&factor W/(m2&K(m/s))
V Voltage V
VOC OpenJcircuit&voltage V
VL Load&voltage V
Vmax,&inverter Maximum&inverter&voltage V
Vmin,&inverter Minimum&inverter&voltage V
VMPP Voltage&at&MPP V
Vz Cell&voltage V
v Wind&speed m/s
Yf Yearly&system&yield kWh
Yr Reference&yield kWh
α Absorption&coefficient J
β Tilt&angle o
βopt Optimum&tilt&angle o
γ Azimuth&angle o
γv Voltage&temperature&coefficient V/oC
δ Declination&angle o
η Efficiency %
ηcell Cell&efficiency %
ηM Module&efficiency %
θ Zenith&angle o
ν Frequency& Hz
ρ Albedo&factor J
ρcable Specific&resistance&of&cable&material Ω&mm2/m
ϕ Latitude o
ωs Hour&angle o
Abbreviations'
!
'
Symbol Explanation
AC Alternating+current
AM Air+Mass
AO Annual+system+operation+cost
BoS Balance+of+System
CIS Copper+Indium+Selenide
DC Direct+current
EMF Electromotive+force
ETA Ethyl+vinyl+acetate
IEC International+electrotechnical+commision
IRR Internal+Rate+of+Return
kWh Kilowatt+hour
kWp Kilowatt+peak
LCOE Levelized+cost+of+electricity MET Norwegian+Meteorological+Institute MonoHSi Monocrystalline+silicon
MPP Maxium+power+point
MPPT Maximum+power+point+tracker NOCT Nominal+Operating+Cell+Temperature
NPV Net+Present+Value
NVE Norwegian+Water+Resource+and+Energy+Directorate PolyHSi Polycrystalline+silicon
PF Packing+factor
PR Performance+Ratio
PV Photovoltaic
RV Residual+value
ST True+Solar+Time
SDR System+Degradation+Rate
STC Standard+Test+Conditions
TSO Transmission+System+Operator UMB Norwegian+University+of+Life+Sciences
Wp Watt+peak
1.'Introduction'
1.1'Motivation'
In! recent! years! a! massive! increase! in! the! installation! of! photovoltaic! (PV)! systems! have! been!
observed.!Driven!by!generous!subsidy!schemes,!the!number!of!both!residential!and!commercial!
PV!systems!has!been!steadily!increasing.!As!a!consequence,!the!costs!of!installing!such!a!system!
have!been!reduced!significantly.!
!
In!Norway!however,!only!a!limited!amount!of!PV!systems!exist!as!of!today.!Most!of!these!are!not!
gridGconnected,! and! are! used! to! produce! limited! amounts! of! electricity! to! offGgrid! cabins! and!
lighthouses.!
!
Through!the!EU!renewable!energy!directive,!Norway!is!committed!to!increase!their!renewable!
energy!share!to!67.5%!by!2020.!A!joint!greenGcertificate!with!Sweden!has!been!introduced!with!
the!goal!of!introducing!26.4!TWh!of!renewable!energy!in!these!two!countries!by!2020[1].!
!
Farms!often!have!large,!southward!facing!roofs!with!limited!surrounding!items!that!could!cause!
shading.!The!local!electricity!consumption!on!farms!is!usually!high!due!to!an!extensive!demand!
for! heating! and! cooling! during! different! seasons.! ! A! roof! PV! system! on! such! farms! could!
contribute!to!an!increase!in!the!renewable!energy!share!and!provide!local,!clean!production!of!
electricity.!
1.2'Objectives'and'Limitations'
The!objective!of!this!thesis!is!to!evaluate!the!possibility!of!installing!a!PV!system!on!a!farm!in!
Rygge.!!Included!in!this!objective!is!the!following:!
!
• To!collect!information!about!the!solar!resource!at!the!site!and!evaluate!the!reliability!of!
these!data.!
• To! evaluate! the! suitability! of! the! different! roofs! considering! an! installation! of! a! PV!
system.!
• To! suggest! possible! system! designs,! and! determine! the! potential! for! PV! power!
production!on!the!farm.!
• To! estimate! the! potential! production! from! the! systems! using! the! simulation! software!
PVsyst,! and! determine! if! the! farm! in! certain! periods! will! become! an! exporter! of!
electricity.!
• To!evaluate!the!economical!consequences!of!installing!a!PV!system!on!the!farm.!
!
This!thesis!is!mainly!written!as!a!feasibility!study,!and!will!therefore!not!go!into!a!great!level!of!
detail!in!matters!such!as!mechanical!dimensioning!of!the!mounting!systems,!earthing!of!the!PV!
systems,!or!rating!of!electrical!components!like!wires!and!fuses.!
1.3'The'Farm'
The!farm!considered!in!this!thesis! is!located!in!Rygge!municipal!in!Østfold,!Norway.!The!farm!
produces!chickens,!vegetables,!potatoes!and!grain.!!
!
The! chicken! production! is! located! in! the! largest! building! on! the! farm.! The! chickens! are!
dependent!on!a!certain!temperature!and!air!quality!in!the!building,!and!the!building!is!therefore!
ventilated!through!15!ventilators!located!on!the!roof.!The!vegetables!produced!on!the!farm!are!
stored!for!distribution,!and!the!farm!therefore!has!a!large!storage!building!for!vegetables.!The!
storage!building!is!cooled!through!an!electrical!cooling!system.!
!
A!new!storage!building!is!also!being!planned,!and!will!most!likely!be!erected!during!the!summer!
of!2013.!!
!
Figure'1:'Panorama'of'the'farm.' !
1.4'Outline'
Chapter! 1! gives! an! introduction! to! the! thesis! and! the! motivation! behind! it,! as! well! as! the!
objectives!and!limitations!and!a!brief!description!of!the!farm!considered!in!this!thesis.!
!
Chapter! 2! provides! an! overview! of! the! different! components! included! in! a! gridGconnected! PV!
system,!with!a!main!focus!on!the!solar!modules!and!their!characteristics,!and!the!inverter!and!
different! inverter! configurations.! Chapter! 3! describes! the! theory! behind! system! design! of!
photovoltaic!systems,!with!a!main!focus!on!tilted!roofs.!!
!
Chapter!4!describes!the!methodology!used!in!this!thesis,!and!the!reasoning!behind!the!choices!
made.!The!simulation!software!PVsyst!is!also!introduced!in!this!chapter.!
!
Chapter! 5! presents! the! results! from! the! simulations,! a! comparison! of! the! simulated! electricity!
production! and! the! local! consumption! and! the! results! of! the! economical! evaluation.! These!
results!are!further!discussed!at!the!end!of!each!subchapter.!
!
Chapter!6!presents!the!main!conclusions!in!the!thesis!based!on!the!given!objectives,!and!chapter!
7!include!suggestions!for!further!work.!Chapter!8!shows!the!references!cited.!!
!
!
!
!
!
!
!
!
!
!
!
2.'Components'in'GridGconnected'PV'Systems'
A! gridGconnected! photovoltaic! (PV)! system! is! dependent! on! several! components! in! order! to!
function.! In! addition! to! the! solar! modules,! which! convert! solar! radiation! to! DC! current,! a!
photovoltaic!system!consists!of!several!Balance!of!System!(BoS)!components!which!ensures!safe!
and!efficient!operation!of!the!system.!
!
A!schematic!of!the!most!important!components!is!shown!in!figure!2.!
!
Figure'2:'Schematic'of'a'grid7connected'PV'system.' !
2.1'Solar'Cells'and'Modules'
The! solar! cell! is! the! fundamental! component! of! the! PV! system! as! it! converts! sunlight! to! DC!
current.! As! the! operating! voltage! of! a! single! solar! cell! is! relatively! low,! several! cells! can! be!
connected!in!series!in!order!to!a!solar!module.!This!chapter!describes!the!basic!concepts!of!solar!
cells!and!modules.!
2.1.1'The'Solar'Cell'
Solar! cells! are! made! of! semiconducting! materials! which! under! the! right! circumstances! can!
produce! electricity! from! electromagnetic! radiation.! As! of! today,! silicon! is! the! most! common!
semiconductor!used!for!manufacturing!solar!cells.!!
!
Semiconducting! materials! are! neither! good! conductors! nor! good! insulators.! Their! electrical!
properties! can! be! understood! through! use! of! the! band! gap! model.! This! model! is! illustrated! in!
figure!3.!!
!
In!the!band!gap!model,!an!electron!can!either!be!fixed!in!the!valence!band,!or!free!to!conduct!in!
the!conduction!band.!The!electrons!in!a!semiconductor!are!fixed!in!the!valence!band.!However,!if!
an!electron!absorbs!an!amount!of!energy!equal!to!the!difference!between!the!conduction!band!
and!the!valence!band,!the!electron!can!be!lifted!from!the!valence!band!to!the!conduction!band,!
and!thus!participate!in!conduction!processes[2].!
!
Inverter
Controller
Local loads
Electricity meters
Utility connections
Array
Figure'3:'Semiconductor'band'structure.'!
In!a!solar!cell,!the!energy!necessary!to!lift!an!electron!into!the!conduction!band!is!provided!by!
energy! from! solar! radiation.! When! a! light! quanta,! also! known! as! a! photon,! is! absorbed! by! an!
electron,!the!electron!is!lifted!into!the!conduction!band!if!the!following!criteria!is!met:!
!
! ℎ!!≥!!!!
!
(2.1)!
Where!h!is!the!Planck!constant,!!!is!the!frequency!of!the!radiation!and!Eg!is!the!band!gap.!
!
Semiconducting!materials!can!be!doped!in!order!to!alter!the!electrical!properties!of!the!material.!
This! is! done! by! adding! either! a! trivalent! or! a! pentavalent! substance! to! the! semiconducting!
material.!If!a!trivalent!substance,!like!Aluminum!or!Gallium!is!added,!a!pGtype!material!is!formed.!
Adding!a!pentavalent!substance,!like!Phosphorus,!gives!a!nGtype!material.!
!
In! order! to! produce! a! current! that! can! be! used! an! external! circuit,! an! electric! field! must! be!
present!to!provide!an!electromotive!force!(EMF).!This!electric!field!is!created!when!a!pGtype!and!
an!nGtype!material!is!connected!to!form!a!pn!junction.!The!excess!positive!charge!carriers!in!the!
pGtype!material!and!the!excess!negative!charge!carriers!in!the!nGtype!material!will!diffuse!to!the!
other!side!of!the!junction,!and!leave!behind!space!charges!which!create!an!electric!field!between!
the!two!materials[3].!!
!
An!illustration!of!a!crystalline!solar!cell!is!shown!in!figure!4.!In!this!figure,!it!is!shown!how!the!
connection!of!a!nGdoped!and!pGdoped!semiconductor!leads!to!a!formation!of!an!electric!field,!and!
how!charge!carriers!are!lifted!into!the!conduction!band!and!mitigates!to!each!side!of!the!field.!
!
!
Figure'4:'Illustration'of'a'crystalline'solar'cell.' !
Valence band
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Eg Conduction band E
- - - - hv > Eg
+ + + + + + +
V -
+ pn junction
E
n-Si
p-Si
+ -
+ +
+ - -
-
!
From!an!electrical!perspective,!the!solar!cell!can!be!represented!using!the!singleGdiode!model.!
This!model!is!shown!in!figure!5.!!Igen!represents!the!charge!carriers!generated!as!photons!hits!the!
solar!cell!and!is!a!function!of!the!global!irradiation!and!the!cell!area.!ID!is!the!diode!current!that!
flows!through!the!pn!junction.!The!series!resistance!Rs!represents!the!voltage!drop!between!the!
point!at!which!the!current!is!generated!and!the!load,!while!the!parallel!resistance!Rp!represents!
leakage!currents!in!the!system.!!
!
Figure'5:'The'single'diode'model'for'a'solar'cell.' !
If!the!resistance!in!the!load!circuit!is!zero,!the!charge!carriers!generated!by!the!sunlight!will!flow!
through!the!external!circuit!in!order!to!recombine!on!the!other!side!of!the!pn!junction.!This!is!
called!the$short(circuit$current,!ISC!,$of!the!solar!cell.!
!
If!the!load!circuit!is!open,!all!the!charge!carriers!generated!will!accumulate!in!the!two!regions!of!
the! junction,! and! hence! reduce! the! electric! field! over! the! junction.! A! forward! diode! current! is!
created!which!is!equal!to!the!current!generated!by!the!photons,!thus!Igen!=!ID!at!this!condition.!
The!voltage!on!the!two!terminals!of!the!solar!cell!is!then!called!the!openGcircuit!voltage,!VOC[4].!!
!
The!power!Pcell!generated!by!the!solar!cell!is!given!by!the!equation:!
!
!
! !!"##=!!!∙!!!
!
(2.2)!
!
where!IL!is!the!current!in!the!external!circuit!in!amperes[A]!and!VL!the!voltage!over!the!external!
circuit!in!Volts[V].!
!
The!maximum!power!point!(MPP)!of!the!cell!is!given!when!the!following!criteria!is!met:!
!
! !!!"## =!!!!!! +!!!!!! =0!
! (2.3)!
!
The!power!output!at!the!MPP!is!then:!
!
! !!"" =!!!""!∙!!!""!
! (2.4)!
The!characteristic!curve!of!a!solar!cell!is!shown!in!figure!6.!
!
Igen ID IRP
IL
RP RL
RS
VL
Figure'6:'The'characteristic'curve'of'a'solar'cell.' ! 2.1.2'Solar'Modules'
Several! solar! cells! can! be! interconnected! to! form! a! solar! module.! A! solar! cell! typically! has! an!
operating!voltage!in!the!range!0.5G0.6!V.!Hence!a!module!with!30!cells!connected!in!series!will!
have!an!operating!voltage!in!the!range!15!–!18!V[5].!!
!
The! cells! in! a! module! are! encapsulated! in! order! to! protect! them! against! the! surrounding!
environment.! The! most! common! encapsulant! is! ethyl! vinyl! acetate! (EVA),! as! this! material! is!
transparent,! stable! at! elevated! temperatures! and! has! low! thermal! resistance.! In! addition,! the!
front!of!the!module!is!usually!covered!by!highly!transparent!glass!and!the!back!by!Tedlar,!which!
is!a!polymer!that!protects!the!cells!from!water!and!water!vapour[6][p.127].!
! !
Solar!modules!can!then!be!connected!in!series!to!form!a!string!of!modules,!and!the!strings!can!
again!be!connected!in!parallel!and!form!an!array!of!modules.!This!is!shown!in!figure!7.!
!
Figure'7:'A'solar'cell,'a'module,'a'string'and'an'array.' !
The!characteristic!curve!of!a!solar!module!changes!with!temperature!and!irradiance!level.!!
The!amount!of!current!generated!in!a!solar!module!is!proportional!to!the!amount!of!sunlight!it!
receives.! The! shortGcircuit! current! ISC! is! therefore! reduced! when! a! module! receives! less!
Voltage [V]
Current [A]
MPP
VMPP IMPP
P = f(V)
VOC ISC
PMAX
Cell Module String Array
irradiance.!This!is!illustrated!in!figure!8,!which!shows!the!characteristic!curve!of!a!solar!module!
under!different!radiation!levels!for!a!constant!cell!temperature.!!
! !
Figure'8:'Characteristic'curves'for'a'solar'module'under'different'irradiance'conditions.'From'PVsyst[7].'
The!operating!temperature!also!affects!the!characteristic!curve!of!a!solar!module.!An!increase!in!
operating! temperature! reduces! the! openGcircuit! voltage! and! the! power! output! of! the! module.!
Figure!9!shows!characteristic!curves!for!a!module!under!different!operating!temperatures!and!
constant! radiation! level.! As! the! voltage! increases! with! reduced! operating! temperature,! the!
output!power!of!the!module!will!also!increase,!which!can!clearly!be!observed!in!the!figure.!
!
Figure'9:Characteristic'curves'for'a'solar'module'for'different'operating'temperatures.'From'PVsyst[7].'!
Incident Irrad = 800 W/m2
Incident Irrad = 600 W/m2
Incident Irrad = 400 W/m2
Incident Irrad = 200 W/m2
50.2 W
29.5 W
19.2 W
9.1 W
Current [A]
Voltage[V]
Cells temp. = 45 C
39.9 W Incident Irrad = 1000 W/m2
Incident Irrad = 1000 W/m2
Current [A]
Voltage[V]
Cells temp. = 30 C, Pmpp = 53.7 W Cells temp. = 50 C, Pmpp = 49.0 W Cells temp. = 10 C, Pmpp = 58.2 W Cells temp. = -10 C, Pmpp = 62.6 W
Cells temp. = 70 C, Pmpp = 44.3 W
2.1.3'Module'Efficiency'
The! module! efficiency! loss! is! the! most! significant! of! the! losses! when! solar! irradiance! is!
converted!to!electricity.!Depending!on!the!type!of!module,!10!–!25%!of!the!irradiation!that!hits!
the!module!will!be!converted.!
!
The!efficiency!of!a!solar!cell!is!given!by!
!
!
! !!"## =! !
!!∙!!!! (2.5)!
!
where!P!is!the!power!output!of!the!cell!in!Watts[W],!G!is!the!irradiance!on!the!cell[W/m2]!and!Az! is!the!cell!area[m2].!!
!
The!module!efficiency!is!
! !! =!!!"##!∙!"!!
! (2.6)!
where!PF!is!the!packing!factor!of!the!module.!The!packing!factor!is!the!ratio!of!the!solar!cell!area!
to!the!total!module!area.!
!
The!solar!module!efficiency!is!limited!by!physical!laws!that!will!not!be!discussed!in!detail!here.!It!
is! however! important! to! mark! that! the! solar! module! efficiency! is! defined! at! standard! test!
conditions!(STC).!The!definition!of!STC!is[8][p.49]:!
• Cell!temperature!of!25℃!
• Irradiance!1000!!/!!!
• Air!mass!(AM)!1.5!
!
The! module! efficiency! is! not! a! constant! size! and! will! change! when! the! operation! conditions!
deviates!from!STC.!
2.1.3'Solar'Cell'Technologies''
There! are! several! different! sola! cell! technologies! available! on! the! market,! although! the! basic!
concept! remains! more! or! less! the! same.! The! different! technologies! vary! in! efficiency! and! cost!
and!have!different!material!properties.!An!overview!of!the!most!common!technologies!including!
their!efficiency,!cost!and!market!share!is!shown!in!table!1.!!It!should!be!noted!that!the!price!of!
solar! modules! is! fluctuating,! and! will! also! depend! on! the! manufacturer! and! the! volume! in!
question.!
!
Table'1:Different'types'of'solar'cells'[4],'[9]'and'[10].'
!
2.2'Inverters'
The! inverter! transforms! DC! current! generated! in! the! PV! array! into! AC! current.! The! most!
important!tasks!for!the!inverter!in!a!gridGconnected!PV!system!is[11]:!
• To!produce!an!AC!current!that!matches!the!frequency!of!the!grid.!
• MPPGtracking!in!order!to!maximize!production!from!the!array.!
!
Type Efficiency[%] Cost1[$/Wp]* Market1share(%)
Monocrystalline-Silicon 17120 1.05 30
Polycrystalline-Silicon 15118 1.05 40
Amorphous-Silicon 5110 0.55 5
CIGS/CIS 11113 0.98 5
CdTE 9111 0.72 10
In! addition! the! inverter! should! provide! safe! and! reliable! operation! over! the! lifetime! of! the!
facility,!typically!20G25!years.!This!includes!avoiding!standGalone!operation!as!this!could!pose!a!
threat!to!people!maintaining!the!grid.!
!
The!inverter!should!have!a!high!efficiency!for!a!broadest!possible!range!of!outputs!from!the!PV!
array[6].!A!typical!efficiency!curve!for!an!inverter!is!shown!in!figure!10.!
!
Figure'10:'Efficiency'curves'for'an'SMA'inverter'for'different'voltage'levels[11].' !
Inverters!can!be!divided!into!different!groups!and!types!related!to!their!technical!specifications.!
They! can! also! have! different! configurations! depending! on! their! size,! and! whether! they! are!
connected!to!the!grid!or!not.!For!a!gridGconnected!system,!there!are!three!main!configurations:!
• Central!inverter!configuration!!
• String!inverter!configuration!
• Module!inverter!configuration!
!
!
Figure'11:'Central'inverter'configuration.' !
The!central!inverter!configuration!is!shown!in!figure!11.!!In!this!configuration,!all!the!strings!in!
the!array!are!connected!to!one!inverter.!Central!inverters!are!cost!efficient!as!only!one!inverter!
is! used! in! the! entire! system.! These! inverters! also! have! a! high! efficiency! for! a! broad! range! of!
array! outputs.! However,! this! configuration! requires! a! significant! amount! of! DC! cabling! that!
increases!array!losses.!It!is!also!sensitive!to!partial!shading,!as!shade!on!one!module!will!affect!
the! performance! of! the! entire! array.! Furthermore,! inverter! failure! will! cause! the! production!
from!the!entire!array!to!be!lost!for!the!entire!inverter!downtime.!
!
Controller Grid
Local loads Central
inverter
Figure'12:'String'inverter'configuration.' !
The! string! inverter! configuration! is! shown! in! figure! 12.! In! this! configuration,! one! or! several!
strings!are!connected!to!one!inverter.!Use!of!a!string!inverter!configuration!reduces!DC!cabling!
and! shading! losses,! on! the! cost! of! a! lower! DC/ACGconversion! efficiency.! A! failure! in! a! string!
inverter!will!only!cause!the!production!from!the!connected!string!to!be!lost,!while!the!rest!of!the!
system! remains! operative.! Some! string! inverters! also! have! several! MPPT! inputs,! which! is! an!
advantage!if!there!are!differences!in!the!performance!of!the!connected!strings.!
!
Figure'13:'Module'inverter'configuration.' !
The!module!inverter!configuration!shown!in!figure!13!has!practically!no!DC!cabling,!and!partial!
shading!losses!are!only!generated!from!partial!shading!on!a!single!module.!Module!inverters!are!
usually!mounted!directly!on!the!back!of!each!module.!However,!this!inverter!configuration!has!
the!lowest!DC/ACGconversion!efficiency,!and!is!therefore!most!suitable!in!PV!systems!with!high!
sensitivity!to!partial!shading.!Module!inverters!are!also!exposed!to!the!weather!conditions!at!the!
installation!site,!and!will!usually!have!a!shorter!lifetime!than!the!modules[6][p.264G265].!
2.3'DC'and'AC'Cables'
DC! cables! are! used! to! connect! the! modules! together,! and! to! connect! an! array! or! a! string! of!
modules!to!the!inverter.!As!the!operating!voltage!in!the!DCGpart!of!the!system!is!relatively!low,!a!
nonGnegligible!ohmic!loss!is!generated!in!the!cables.!!Furthermore,!the!voltage!drop!in!the!cables!
could!affect!the!operation!of!the!inverter.!
!
Controller Grid
String inverter
String inverter Local loads
Controller Grid
Local loads Module
inverter
DC! cables! are! expensive.! The! cable! route! of! the! system! should! hence! be! designed! in! order! to!
minimize! the! use! of! DC! cables.! Losses! in! the! cables! can! be! limited! by! increasing! the! crossG sectional!area!of!the!cable,!although!this!measure!will!increase!the!cable!cost.!
!
The!DC!cables!are!exposed!to!the!local!climate!and!should!be!insulated!and!protected.!Cables!are!
typically!rated!for!different!temperatures,!sunlight!and!water!resistance,!and!special!cables!have!
been!designed!for!use!in!PV!systems[8][p.147G148].!
!
Depending! on! the! distance! from! the! inverter! to! the! grid! injection! point,! there! could! also! be!
significant!losses!in!the!AC!cables.!AC!cables!will!often!be!more!shielded!from!the!climate!than!
the!DC!cables,!and!in!the!cases!of!short!distance!between!the!inverter!and!the!injection!point,!AC!
losses!are!sometimes!considered!negligible.!Nevertheless,!attention!should!be!paid!to!the!length,!
crossGsectional!area!and!quality!of!the!AC!cables!as!well.!
2.4'Mounting'Systems'
A!mounting!system!for!the!PV!modules!is!required!to!ensure!safe!operation!of!the!system!at!all!
times.! There! are! a! large! amount! of! different! solutions! available! for! mounting! of! PV! modules,!
depending! on! whether! the! system! is! building! integrated! (BIPV),! building! applied! (BAPV)! or!
ground!mounted.!!
!
A! PV! mounting! system! should! meet! several! criteria.! The! system! must! be! able! to! support! the!
weight!of!the!modules,!and!additional!loads!from!weather!such!as!wind!and!snow.!Furthermore,!
the!mounting!system!should!be!designed!to!provide!ventilation!of!the!modules,!as!power!output!
is!reduced!when!the!operating!temperature!of!the!modules!are!increased[8][p.85G98].!!
!
For!BIPV!and!BAPV!systems,!the!weight!of!the!mounting!system!itself!is!an!important!factor.!It!is!
preferable! that! the! mounting! system! does! not! penetrate! the! membrane! of! the! roof,! as!
penetration!will!increase!the!risk!of!water!leaking!into!the!building[6][p.166G174].!
!
!On!pitched!roofs!there!will!in!most!cases!be!used!a!mounting!system!with!the!same!tilt!angle!as!
the!original!roof!angle.!Brackets!or!bolts!are!used!to!mount!the!modules!to!cross!beams!slightly!
above! the! roof! surface! to! allow! for! air! to! circulate! between! the! roof! and! the! modules.! An!
illustration!of!a!mounting!system!for!a!tilted!roof!is!shown!in!figure!14.!
!
Figure'14:'Illustration'of'a'PV'mounting'system'for'tiled'roofs[12].' !
2.5'Other'BoS'Components'
Other!balance!of!system!(BoS)!components!are!used!in!a!gridGconnected!PVGsystem!to!maximize!
the! lifetime! of! the! system! and! ensure! optimal! operation.! In! addition! to! the! components!
described!earlier,!BoS!components!will!typically!include!those!described!in!this!chapter.!!
2.5.1'Protection'and'Disconnect'Switches'
Several! components! are! installed! in! order! to! protect! the! system! from! being! damaged! by!
!
Disconnection!switches!are!usually!installed!on!both!the!DC!and!the!AC!side!of!the!inverter,!and!
must! often! meet! specific! requirements! set! by! the! government! or! the! grid! operator.! ! The!
disconnection! switches! allow! the! power! in! a! circuit! to! be! shut! down.! On! the! ACGside! of! the!
inverter,!a!utility!external!disconnect!switch!is!also!installed!in!gridGconnected!systems!in!order!
to!avoid!standGalone!operation!of!the!PV!system!when!the!grid!is!down[8].!
!
Fuses!and!circuit!breakers!are!also!widely!used!to!protect!the!system!against!overGcurrents.!DC!
currents!are!more!difficult!to!break,!as!they!do!not!pass!through!a!zero!voltage!point.!DC!current!
circuit!breakers!are!thus!more!complicated!and!expensive!than!AC!current!breakers.!!
!
Lightning! protection! may! also! be! required! in! some! cases,! both! on! the! DC! side! to! protect! the!
system!against!strikes!on!the!array,!and!on!the!AC!side!to!protect!it!against!strikes!in!the!grid.!!
2.5.2'System'Monitoring'and'Metering'
A! PV! system! also! needs! a! system! to! monitor! important! system! parameters! like! voltage,!
frequency,!time,!temperature!and!energy!production.!This!system!is!usually!an!integrated!part!of!
the!inverter.!
!
A!gridGconnected!system!will!also!need!a!metering!system!which!registers!the!amount!of!energy!
produced,!and!whether!the!energy!is!consumed!at!the!site!or!is!fed!into!the!electric!grid.!
!
There! are! two! different! ways! for! a! utility! company! to! measure! the! amount! of! electricity!
delivered!to!the!grid!by!the!PV!system:!Net!metering!and!gross!metering.!!
!
Figure'15:'Schematic'of'the'net'metering'system'and'the'gross'metering'system.' !
When! using! net! metering! the! utility! measures! the! net! difference! between! the! amount! of!
electricity!exported!and!imported!for!the!site.!If!the!exported!and!imported!amount!are!equal,!
the!customer!does!not!pay!anything!to!the!utility!company.!If!the!customer!is!a!net!exporter!in!
the!given!period!it!will!get!paid!for!the!net!excess!generation.!In!the!opposite!case!the!customer!
will! pay! for! the! net! consumption! of! electricity.! From! a! technical! point! of! view! this! can! be!
achieved!by!letting!the!meter!run!backwards!in!periods!of!export.!The!netGmetering!system!is!
illustrated!to!the!left!in!figure!15.!
!
When! the! gross! metering! method! is! used! the! production! and! consumption! is! measured!
separately,! and! the! import! meter! and! export! meter! run! separately.! This! system,! which! is!
illustrated!to!the!right!in!figure!15,!allows!for!differentiated!pricing!of!electricity!depending!on!
time!of!day,!spot!price!or!other!factors,!and!is!the!system!currently!being!used!in!Norway[8].!
Grid
Net import
meter
Loads PV system
Loads PV system
Grid
Generation meter
Consumption meter
Net metering Gross metering
3.'Theory:'Design'and'Optimization'of'GridGconnected'PV'systems'
In! this! chapter,! the! most! important! factors! to! consider! when! designing! a! gridGconnected! PV!
power!system!are!described.!!
!
Chapter! 3.1! describes,! in! brief,! how! a! site! assessment! can! be! conducted! when! considering!
installation!of!a!PVGsystem.!!
!
Chapter! 3.2! provides! a! theoretical! background! to! the! solar! resource! and! how! the! resource! is!
evaluated!for!a!potential!PV!system!site.!
!
In! chapters! 3.3! to! 3.5,! the! influence! of! module! orientation,! shading! and! system! design! on! the!
performance!of!a!PV!system!is!explained,!while!chapter!3.6!presents!the!most!common!system!
losses!and!different!parameters!that!are!used!in!the!evaluation!of!a!PV!system´s!performance.!
!
In!chapter!3.7,!an!introduction!to!the!regulatory!regime!in!Norway!and!methods!for!evaluating!
the!economics!of!a!PV!system!are!presented.!
3.1'Site'Assessment'
A!site!assessment!is!usually!conducted!in!the!initial!phase!of!a!PV!system!development!project.!
The!purpose!of!such!an!assessment!is!to!get!an!overview!over!key!factors!that!will!influence!the!
performance!of!the!system.!After!the!initial!assessment,!a!detailed!design!of!the!system!can!be!
made!considering!the!factors!described!in!this!chapter.!
!
For! a! roof! PV! system,! the! following! information! is! usually! collected! during! an! initial! site!
assessment[8]:!
• Possible!locations!of!the!PV!array!
• Roof!specifications,!including!orientation!and!tilt!angle!
• Shading!items,!like!trees,!vegetation,!buildings!and!roof!components!
• Available!area!for!PV!installation!
• Possible!mounting!system!
• Possible!location!of!BoS!components!
!
If! available,! an! assessment! of! the! local! electricity! consumption! should! be! made! in! order! to!
compare!possible!production!and!consumption!for!the!site.!!This!relationship!could!be!of!great!
importance!in!cases!where!there!is!a!different!economical!value!to!a!kWh!delivered!to!the!grid!
compared!to!a!kWh!consumed!at!the!production!site.!!
3.2'Solar'Radiation'and'Meteorology'
The! amount! of! electricity! produced! by! a! photovoltaic! system! will! depend! on! the! amount! of!
irradiation! that! the! PV! modules! receive.! An! assessment! of! the! solar! radiation! and! the!
meteorology!on!the!planned!installation!site!is!therefore!of!great!importance!when!optimizing!a!
photovoltaic!system.!
!
At!the!edge!of!the!earth´s!atmosphere,!the!solar!irradiance!has!approximately!the!same!value!at!
a!plane!that!is!perpendicular!to!the!direction!of!the!sun.!The!average!irradiation!value!is[6]:!
!
!!=1367!±2!!/!!!
!
!!!is!also!known!as!the!solar!constant.!
!
However,!at!the!earth´s!surface!the!irradiance!will!vary!significantly,!mainly!due!to!atmospheric!
effects,!latitude,!season!of!the!year!and!the!time!of!day[3].!
3.2.1'Season'of'the'Year'and'the'Time'of'Day'
The!earth!uses!365!days!to!orbit!the!sun!and!24!hours!to!rotate!around!its!own!axis.!At!a!given!
location,!the!solar!irradiance!will!therefore!arrive!from!different!directions!at!different!times!of!
the!day!and!year.!!
!
The! motion! of! the! Earth! around! the! sun! is! tilted! by! 23.45°!to! the! equator.! In! the! Northern!
hemisphere,!the!Earth!will!be!tilted!away!from!the!sun!in!the!period!from!autumnal!equinox!to!
vernal! equinox,! and! tilted! towards! the! sun! from! vernal! equinox! to! autumnal! equinox.! The!
declination! angle,!!,! is!23.45°!at! summer! solstice,!−23.45°!at! winter! solstice,! and!0°!at! the! two!
equinoxes[5].!The!variation!in!declination!angle!through!the!year!is!illustrated!in!figure!16.!
!
!The!sun´s!change!in!path!during!the!day!is!described!using!the!hour!angle,!!!,!which!is!the!angle!
between! the! meridian! of! the! site! and! the! meridian! of! the! Sun.! This! angle! is! by! definition!0°!at!
solar! noon.! The! hour! angle! can! be! calculated! using! equation! 3.1.! Note! that! the! hour! angle! is!
negative!in!the!morning!and!positive!in!the!afternoon.!
!
! !! = !"−12 ∙15°!
!
(3.1)!
where!ST!is!the!local!time!in!hours.!!
!
Figure'16:'The'Earth´s'declination'angle'for'different'times'of'the'year.' ! 3.2.2'Latitude'and'solar'elevation'angle'
The!latitude!!!of!a!site!determines!the!highest!elevation!angle!of!the!sun!through!the!year!and!
for! each! day.! The! highest! elevation! is! not! constant! through! the! year,! and! in! the! Northern!
Hemisphere!the!elevation!will!be!highest!at!solar!noon!on!summer!solstice.!
!
The! elevation! of! the! sun! is! denoted!ℎ!.! The! following! relation! is! given! between!ℎ!,!!,!!!and!!!! [3][p.96]:!
!
! sinℎ!=sin!sin!+cos!cos!cos!!! (3.2)!
!
Autumnal equinox Sept 23
S
N N
N
N S
S S
Vernal equinox March 21
Winter solstice December 21 Summer solstice
June 21 δ = 23.45
!!
!!
δ = 0
!!
!!
δ = 0
!!
!!
δ = -23.45
!!
!!
Equation!3.2!shows!that!the!solar!altitude!varies!depending!on!three!factors:!The!time!of!year,!
which!is!expressed!through!the!declination!angle,!!,!the!site!location,!through!the!latitude,!!,!and!
the!time!of!day!represented!in!the!hour!angle,!!!.!
Figure'17:'Illustration'of'the'elevation'angle'h.' !
When!the!latitude,!hour!angle!and!declination!angle!of!a!given!site!is!known,!the!extraterrestrial!
irradiance!for!the!location!at!any!given!time!can!be!calculated!using!the!equation[6][p.31]:!
!
! !!"=!!!"!∙sinℎ!! (3.3)!
!
Where! Gex! is! the! extraterrestrial! irradiance! on! a! horizontal! plane! [W/m2]! and! Sex! is! the!
instantaneous!solar!constant!varying!between!1322!and!1414!W/m2!depending!on!the!time!of!
year.!
3.2.3'Atmospheric'Effects'
Different!atmospheric!effects!like!scattering,!absorption!and!reflection!influence!the!magnitude!
of! the! power! received! at! the! Earth´s! surface,! and! also! change! the! characteristics! of! the!
irradiance.!The!properties!of!the!irradiation!on!ground!level!can!thus!be!very!different!from!the!
extraterrestrial!irradiation.!!
!
As! solar! radiation! passes! through! the! atmosphere,! components! like! CO2,! O3! and! water! vapour!
(H2O)! will! absorb! some! of! the! radiation,! while! some! radiation! is! scattered! back! to! space! or!
towards!the!earth.!!
!
The! atmospheric! effects! on! the! solar! radiation! will! depend! on! the! composition! of! the!
atmosphere!and!the!length!of!the!path!that!the!radiation!has!to!travel!through!the!atmosphere.!
The!path!length!is!often!described!using!the!air!mass!(AM)!concept,!which!is!illustrated!in!figure!
18![3][p.98].!!
!
! !"= 1
cos!!
!
(3.4)!
where!!!is! the! angle! between! zenith! and! the! sun.! AM0! refers! to! zero! atmosphere! irradiance,!
which!is!the!extraterrestrial!irradiance!at!the!edge!of!the!atmosphere.!
!
hs
N
S E
Zenith
Figure'18:'Illustration'of'the'Air'Mass'(AM)'concept.' !
Figure! 19! shows! how! the! irradiance! spectrum! changes! due! to! atmospheric! effects! at! AM1.5,!
compared!to!the!extraterrestrial!irradiance.!As!shown!in!equation!2.1,!the!current!generated!by!
the! sun! is! dependent! on! the! wavelength,! and! thus! the! frequency,! of! the! irradiance.! The!
performance! of! a! solar! module! will! thus! change! through! the! day! as! the! irradiance! spectrum!
changes.!
!
Figure'19:'Irradiance'spectrum'for'extraterrestrial'irradiance'and'irraance'at'AM1.5[13].' !
When!the!irradiance!passes!through!the!atmosphere,!two!of!the!atmosphere´s!main!components,!
CO2!and!H2O!absorbed!practically!all!the!irradiance!at!certain!frequencies.!O3!absorbs!radiation!
in! the! ultraviolet! (UV)! part! of! the! spectrum.! Rayleigh! scattering,! which! is! caused! by! small!
particles!in!the!atmosphere,!also!affects!the!irradiance!spectrum[4][p.110].!
!
The! total! amount! of! irradiation! received! at! a! given! site! at! the! Earth´s! surface! is! given! by! the!
equation:!
!
! !! =!!!+!!!+!!!! (3.5)!
!
!
Air mass (AM) = 1 θ
Air mass (AM) = 1/cos θ
!!
0.0#
0.5#
1.0#
1.5#
2.0#
2.5#
280# 330# 380# 460# 560# 660# 760# 860# 960# 1060#1160#1260#1360#1460#1560#1660#1995#2495#2995#3495#3995#
Spectral)power)density[W/m2)nm])
Wavelength[nm])
AM1.5#
AM0(Extraterrestrial)#
O3
H2O
H2O,&&O2 H2O
H2O,&CO2
Where!HG!is!the!total!amount!of!irradiation,!often!referred!to!as!global!irradiation,!expressed!in!
the! unit! Wh/m2/day,! MJ/m2/day! or! kWh/m2/year.! HB! is! the! direct! beam! component! of! the!
global!irradiation!which!passes!through!the!atmosphere!without!being!absorbed!or!scattered.!HD! is!the!diffuse!component!which!is!first!absorbed!and!later!reemitted!from!the!surroundings.!HR! is!radiation!that!is!reflected!from!the!surroundings.!This!threeGcomponent!model!is!illustrated!in!
figure!20.!
!
!
Figure'20:Different'components'of'solar'radiation.' !
HR!is!a!function!of!the!total!amount!of!solar!radiation!hitting!the!surface!as!well!as!the!albedo,!!,!
of!the!surroundings.!It!is!calculated!using!the!equation!
!
! !! =!!!∙(!!+!!!)! (3.6)!
!
The! albedo! is! a! reflection! factor! indicating! how! much! of! the! irradiation! that! is! reflected! of! a!
surface.! An! albedo! value! of! 1! indicates! that! all! the! radiation! that! hits! the! surface! is! reflected,!
while!a!value!of!0!indicates!that!all!the!radiation!is!absorbed.!!
!
!A!table!of!representative!albedo!values!for!different!surroundings!is!shown!in!table!2.!
!
Table'2:'Albedo'values'for'different'surfaces[6].'
Earth´s surface Reflected solar
radiation from atmosphere
Cloud Top of atmosphere
Direct beam Diffuse Reflected
Surface Albedo
Asphalt 0.14540.15
Green4forest 0.14540.2 Wet4ground 0.14540.2 Dry4ground 0.154540.3 Glass5covered4ground 0.24540.3
Concrete 0.24540.35 Desert4sand 0.34540.4
Old4snow 0.54540.75 Newly4fallen4snow 0.754540.9
3.2.4'Collection'and'Assessment'of'Meteorological'Data''
Collection! of! accurate! meteorological! data! is! one! of! the! important! tasks! when! designing! a! PV!
system,!as!the!system!yield!will!be!highly!influenced!by!the!amount!of!irradiation!received!by!the!
modules.!Meteorological!data!can!be!divided!into!two!categories:!Data!collected!from!weather!
stations,!and!data!collected!from!databases!based!on!interpolation!between!different!sources!or!
satellite!data.!!
!
The!format!of!the!data!will!also!vary!between!the!different!sources.!Weather!station!data!could!
typically!be!hourly,!daily!or!monthly!time!series.!An!example!of!an!hourly!time!series!is!shown!in!
figure!21.!
!
Figure'21:'Irradiance'values'registered'on'March'14th'at'a'weather'station'in'Ås.'!
In!many!cases!there!are!a!limited!number!of!weather!stations!near!a!site,!and!even!fewer!may!
hold!reliable!data!sets!for!irradiation!data.!The!use!of!databases!in!order!to!collect!metrological!
data!for!a!specific!site!is!common,!and!a!variety!of!different!databases!exist!that!allows!for!siteG specific!collection!of!weather!data.!Databases!in!most!cases!provide!yearly,!monthly,!daily!or!in!
some! cases! hourly! average! irradiation! values.! An! irradiation! map! from! the! PVGIS! database! is!
shown!in!figure!22.!
!
Figure'22:'Map'from'PVGIS'showing'average'global'irradiation'values'for'Europe[14].' !
0"
100"
200"
300"
400"
500"
600"
1" 2" 3" 4" 5" 6" 7" 8" 9" 10" 11" 12" 13" 14" 15" 16" 17" 18" 19" 20" 21" 22" 23" 24"
Irradiance[W/m2]/
Hour/
Irradiance"values"on"March"14th"
